Process for recovery of cyclopentadiene



AP 21, 1953 H. F. JOHNSON, JR 2,636,054

PROCESS FOR RECOVERY OF CYCLOPENTADIENE Filed Aug. 25, 1947 2 $HEETS$HEET 2 H EAT EIL F I GE'Z Homer Jobmeorzpff Ira amberbz MCLttoEp. as

Patented Apr. 21, 1953 PROCESS FOR RECOVERY OF CYCLO PENTADIENE Homer F. Johnson, Jr., Union, N. J assignor to Standard Oil Development Company, a corporation of Delaware Application August 25, 1947, Serial No. 770,456

'7 Claims. 1

This invention relates to a practical method of obtaining monomeric cycloalkadienes of high purity from cracked petroleum oils. More par ticularly it relates to an improved process for the recovery of high purity cycloalkadiene monomers by means of liquid phase depolymerization of cycloalkadiene polymers contained in low concentrations in an aromatic naphtha.

Cyclopentadiene is a highly reactive cyclic diene which has a potentially large scale demand for use as a modifier for drying oils, as a reactant in the manufacture of resinous copolymers and in the preparation of textile impregnating agents. Additional suggested uses are dependent upon a commercially available supply in a relatively pure state. Commercially available supplies in the past have been of only limited purity.

There has grown up during recent years a demand for normally gaseous unsaturated hydrocarbons such as ethylene and butadiene. Intensive cracking processes have been developed for converting large proportions of petroleum feed stocks to these gases. These processes also yield naphtha distillates that contain considerable amounts of aromatic compounds mixed with unsaturated hydrocarbons. An intermediate distillate fraction, such as a cycle gas oil, and a heavy tar are also obtained. Conditions favorable for obtaining high yields of unsaturated hydrocarbons and aromatics in cracking volatile petroleum stocks are high temperatures of the order of 1200 to 1500 F. and low pressures of the order of 1 to 10 atmospheres.

The charging stock for this operation is fed to the cracking zone where it may be diluted with up to 90% mol percent of steam in order to restrict carbonization. The hot cracked product issuing from the cracking zone is quenched and fed to a fractionating tower. The naphtha fraction and steam are then taken off overhead leaving the residual oils which are taken off as tarry bottoms and a cycle gas oil which is taken off as a side stream. The fractionated naphtha and steam are cooled and a water layer is separated. By processing the highly cracked products in the manner described, the cycloalkadienes are found in this naphtha fraction mainly as polymers. The amount of cycloalkadiene polymers in this final naphtha fraction seldom exceeds 12%.

Depolymerization of the dimer has been performed directly on this naphtha feed after the conventional debutanization as one of the steps In either case vapor phase cracking of this naphtha distillate is a relatively high cost operation, and requires expensive equipment, including additional equipment for separating impurities.

The vapor phase depclymerization of cycloalkadienes in a wide naphtha fraction is difficult to control, and necessitates repolymerization of the monomer for cracked components. Because some of these other components, i. e. other C 5 diolefins and, some C 6-8 constituents, polymerize also, the

the naphtha. Another object of this invention is to provide a more rapid and efficient liquid phase process for depolymerization of cycloalkadiene polymers. Other objects will be apparent to those skilled in the art.

This invention is a method or separating-and recovering a cycloalkadiene monomer such as cyclopentadiene from a cracked petroleum naphtha stock containing its polymers which com prises the steps of fractionally distilling the naphtha stock with steam to remove at least its C1 through C5 hydrocarbon but preferably its Ci through a major proportion of its Ca hydrocarbons to leave a topped aromatic fraction boiling about 350 F., heating the topped aromatic fraction at its boiling point in the liquid phase in a heat treating zone to depolymerize the dimers,

stripping with hot vapors to remove cycloalka diene monomers from the hot aromatic fraction as rapidly as formed, quickly fractionally distilling the overhead product so that substantially all of the monomer is taken all? overhead and returning heavier materials containing any repolymerized monomer to the heat treating zone .for further depolymerization.

Having outlined the process of this invention in a general manner, further specific details will be explained with reference to the accompanying drawings.

Fig. 1 is a flow diagram which schematically illustrates means and steps in carrying out a 1 preferred embodiment of this invention.

Fig. 2 is a vertical section of a two-stage heating zone 23 of Fig. 1 shown in further detail.

In the flow diagram I represents a high tem- 1 perature steam cracking zone into which a pctroleum cracking stock is charged from line 2 obtaining separation of other 3 and steam or preheated water is supplied from line 3, the charging stock being in the liquid or preheated vapor condition. The cracking zone may be contained in a fired pipe coil or other conventional type of cracking aparatus. Steam or preheated water may be supplied at a multiplicity of points to the coil. The cracked products leave the cracking zone through line 4 and are promptly quenched by introduction of cool liquid cycle oil introduced by line 5 into line 4. The quenched cracked products are discharged from line 4 into a fractionating zone 6 from which.

cracking tars are withdrawn through line 1, and liquid cycle oil is withdrawn as a side stream, line 8. Cracked naphtha vapors together with steam and gases are drawn overhead from fractionating zone 6 through line 9 and are passed through cooling condenser it? into a separation zone H. Uncondensed gases leave the separation zone through line 12. Water condensate is removed from the bottom of the separation zone through line l3 and naphtha distillate which may include varying amounts of condensed C1 to C12 hydrocarbons is withdrawn through line It from the separation zone H to a fractional distilling means [5.

The unoondensed gases withdrawn from the 7 separation zone I! through line l2 may be compressed in compressor IE partially condensed in condenser and sent to separator 42. Inert non=condensible gas is Withdrawn overhead through it and the condensate is combined by line I! with the distillate supplied to the fractionating means l5 for the common fractionation therein.

This feed to fractionator l5 conventionally is first debutanized and the overhead fraction used as a feed for other processes.

In the fractionating means E5, the naphtha distillate is kept at as low a temperature as possible during removal of C4 through C7 hydrocarbons to minimize decomposition of cycloalkadiene polymers. Live steam is introduced through line 18 in order to lower the distillation temperatures of the hydrocarbons to be stripped. The gases taken overhead through line l9 comprise up to C8 hydrocarbons, steam, very little cyclopentadiene monomer and some aromatics. This overhead fraction may then also be used as a feed for other processes, or fractionated elsewhere. The thus topped aromatic distillate is Withdrawn as bottoms from the fractionating tower it: through line 20, and advantageously free from any water, is passed through heater 2| and then to a two-stage heating zone 23 through line 22.

The withdrawn bottoms from fractionator I5 is generally at a temperature of about 250-275 F. The heater 2| brings the temperature up to about 330-350 F., and the thus heated bottoms are transferred through line 22 to a point near the top of the first zone 25 of the two-zone heating means 23. (Shown in detail in Fig. 2.) The thus heated bottoms accumulate in the first zone 24 until the liquid exceeds the height of the entrance to the liquid downcomer 25. The liquid continuously thereafter flows down to the second stage of the heating zone 25, is heated by i'eboilers 27 and 28 to about 350-380 F. and returns through lines 29 and 30 to the second heating zone '26; The liberated monomers rise along with other vapors through vapor line 3'! and are bubbled through the liquid in the first stage by means of perforated plate distributor 35-, which located above solid plate 44, which separates the two zones. This accomplishes stripping of the cyclopentadiene formed in the first stage. Operating conditions for the first stage are preferably 320-360 R, pressure conveniently d p. s. i. gauge, and for the second stage 340-375" R, conveniently 10 p. s. i. gauge. The remaining high boiling naphtha freed of polymers of cyclopentadiene and its homologs is Withdrawn from heating zone 23 as bottoms by line 31. The usual duration of this described heat treatment in the liquid phase is four to eight hours.

The vapors taken off overhead by line 32 are condensed by condenser 33 to below 300 F. and are then taken to fractionating means 34. The monomers are cooled as quickly as possible after depolymerization. The distillation of the heat treatment product following the condensation is carried out in such a manner as to minimize polymerization of cycloalkadi'e'ne monomer, and preferably follows the condensing immediately. Hold-up time in the distillation and fractionation is minimized. The temperature of overhead vapors from fractionating means 34 should not exceed 120 F. and preferably runs about 106 F. or lower depending on cooling water temperature available. The bottoms from fractionating means 34 are recycled by line 36 by means of a pump or gravity flow to the first stage 24 of a heating zone 23 and any redimerized monomer is not lost. 7

The cyclopentadiene vapors are Withdrawn overhead from fractionating means 34 through line 38 and cooler 39 into receiver 49 for the cyclopentadiene monomer cut. Higher boiling homologs may also be Withdrawn.

Particular points of interest in the preceding detailed description are as follows:

In the removal of the C4 to Ca material in fractionator l5 steam distillation is used. Removal of these hydrocarbons is highly desirable so that substantially pure monomer can be recovered and more efiicient operation can be obtained in the subsequent operations. It has been found that if only a small portion of feed stock were topped in the fractionation, i. e., C410% C5, the lighter hydrocarbons would later appear in significant quantities in the vapor being removed from heating zone 23. Increasing the hydrocarbons taken overhead from Cato 10% C6, to C2 to 90% C8 reduces the amount of vapor subsequently taken overhead from the heating zone 23 by a factor of about 15. This results in a decrease in the vapor requirement to remove monomer from the heat treating zone and consequently necessitates less heat input. Lower pressures can then also be used. In addition the increased concentration of the cycloalkadiene polymer greatly decreases the holdup volume required in the heat treating zone.

order to secure the removal of C4 through 90% C8 material without danger of dicycloalkadiene 'depolymerization. At a bottom temperature of 284 F. only 0.1 of one percent cyclopentadiene monomer is found in the overhead product. If this temperature exceedsSOO R, as much as 5% monomer can be found in the overhead product. Vapor pressure of Water at 284 F. is 37.7 p. s. i. gauge and a tower operated at this pressure cannot reach a temperature above this figure as long as a liquid water phase is present. When the tower is kept at 266 F., 26 .p. s. 1. gauge, however, up to 90% of the C8 hydrocarbons are removed. The amount taken overhead in this separation was 73 volume percent of the debutanized feed going to this tower.

The feed going to the heating zone 23 comprises largely alkyl substituted aromatic homologs of benzene and cycloalkadiene polymers. The initial boiling point of this aromatic fraction is about 365 F. The higher concentration of dimer in this aromatic naphtha due to the prior removal of C1 through 90% Ce hydrocarbons enables the depolymerization of the dimer to proceed much more rapidly in the heat treatment. The use of the two heating zones 24 and 26 also contributes to this more rapid operation. The dimer concentration in the first zone 24 is higher than in the second zone 26. The formation of the monomer thereby proceeds more rapidly. It is necessary to almost completely remove the monomer to prevent its repolymerization. The vapors from the liquid in the second zone sweep through the liquid in the first zone and the monomer is removed rapidly overhead, thus preventing its redimerization. The amount of vapor required to remove the monomer from the upper section of the reactor increases with any increase in the lighter before mentioned hydrocarbons in the feed. Using two stages instead of one in heating zone 23 in order to depolymerize 90% of the dimer, reduces the required heating time by about one-half. The described stripping of monomer vapors as formed from heating zone 23 can also be accomplished by the use of steam or any inert gas.

A multi-stage process may be used instead of a two stage heating zone. The vapors from each stage maybe bubbled up through the liquid of the preceding stage, heat being put only into the last stage. This is equivalent to a counter current stripping operation.

The fraction taken overhead from tower 34 depends on the product desired, thus a cut through C5, C6 or C7 may be taken overhead depending on the final product desired. It is desirable to keep this polymerization in the final tower to a minimum. This is accomplished by designing the tower for minimum holdup and minimum temperature of operation in the upper section where the monomer is concentrated.

In a manner similar to that described for obtaining the cyclopentadiene monomers, its homologs such as methyl cyclopentadiene, dimethyl cyclopentadiene and cyclohexadiene can also be separated and recovered from the cracked petroleum products.

Experimental data were obtained in investigating cyclopentadiene monomer recovery in a two stage heating zone operation performed in the manner described and the tabulated results are presented in the following table:

TABLE Liquid phase cyclopentadz'ene recovery Product Yield,

Il rodkict on y Mol Percent Temperature Range in Heat Treating Zone Heating Zone Residence Time, Hours Vol.

Percent to preferred modifications and adaptations but it is to be understood that other modifications come within the scope of this invention as defined in the appended claims.

I claim:

1. A continuous process for forming and separating a monomeric cycloalkadiene from a cracked petroleum naphtha fraction containing the cycloalkadiene dimer, said naphtha fraction having been topped to remove monomeric diolefins and C7 and lower hydrocarbons that boil beportion of the topped naphtha fraction continuously thereto; heating said residual liquid porl tion from the first heating zone in the liquid phase in the second heating zone to depolymerize the cycloalkadiene dimer which said residual liquid portion contains and to form vapor of its monomer; sweeping hot vapor containing the monomer vapor from said second heating zone to said first heating zone to strip additional cycloalkadiene monomer therefrom, taking off the combined vapors from said first zone to a fractionation zone separate from any zone in which initial naptha fraction is topped; fractionating the cycloalkadiene monomer from the vapors entering said fractionation zone in the absence of C1 and lower hydrocarbons other than cycloalkadiene monomer to obtain a distillate product of the monomer, and returning a bottoms portion from said fractionation zone to said first heating zone for further recovery of monomeric cycloalkadiene.

2. A continuous process for separating and recovering a monomeric cycloalkadiene from a cracked petroleum naphtha fraction containing the cycloalkadiene polymer, which comprises the steps of steam-distilling the cracked petroleum naphtha fraction to remove C4 through C7 hydrocarbons therefrom at below 300 F. so as to leave a topped aromatic fraction with negligible change in the amount of the cycloalkadiene polymer therein; passing said topped fraction to the first of the series of two heating zones, the first zone being in communication with a second heating zone so as to supply a residual liquid portion of the naphtha fraction continuously thereto; heating the residual liquid portion from the first heating zone in the liquid phase in the second heating zone to depolymerize the cycloalkadiene polymer and vaporize cycloalkadiene monomer; sweeping hot vapor containing the vaporized monomer from said second heating zone to said first heating zone to strip additional cyclo alkadiene monomer therefrom; taking off the resulting combined vapors from said first zone to a fractionation zone separate from any zone in which initial naphtha fraction is topped through a cooling zone wherein said vapors undergo quick condensation, and fractionating the cycloalkadiene monomer in the absence of 04 through C7 hydrocarbons other than the cycloalkadiene monomer from the resulting condensate.

3. A continuous process for separating and recovering a monomeric cycloalkadiene from a cracked petroleum naphtha fraction containing the cycloalkadiene dimer with lower boiling dienemies" olefin monomers, which .comprises th'e 'steps of distilling said'lower boiling monomers and C? and lower hydrocarbons. from the cracked petroleum naphtha fraction toleavea' topped naphtha fraction containing substantially the same amountr'of :cycloalkadiene dimer as contained by the-naphtha prior to this topping step; passing-said topped fraction'to the first of the series of'two heating zones, the first zone being in communication with a second heating zone, so as tosupply a residual liquid portion of the naphtha fraction thereto; heating the residual liquid aro matic fractionsfrom the first heating zone in the liquidphase in the second heating zone to depolymerize the cycloa-lkadiene dimer and form cycloalkadiene monomer vapor; passing vapor from said second heating zone to said first heating none to strip additional cycloalkadiene monomer therefrom; taking off 'the combined vapors from said first zone to a fractionation zone separate from any zone in which initial naphtha fraction is topped; cooling the vapors as they pass to the fractionation zone and distilling the cycloalkadiene monomer in the absence of C7 and lower hydrocarbons from the fractionation zone.

4. A process as inclaim 3, in which a temperaturein the range -of 320 to 360 F. maintained in the first heating zone and a temperature in the range "of 340 to 375 F. is maintained in the second heating zone.

Bra-processes in cla-im 3, in which the monomeric cycloalkadiene is cyclopentadiene.

6. A process as in claim 3, in which the monomeric cycloalkadiene its-methyl cyclopentadiene.

7. A continuous process of forming and separating a monomeric cycloalkadiene from a cracked petroleum. naphtha. fraction containing the cycloalkadiene dimer, said naphtha fraction having been topped to-remove monomeric 8. diolefins and other hydrocarbons that boil below 350 R, which comprises passingsaid topped fraction containing substantially the same amount of the cycloalkadiene dimer as was present in the naphtha fraction prior to thetopping to the first of a series of two heating zones where said dimer undergoes depolymerization, the first. heating zone being in communication witha second heating zone so as to supply a residual liquid portion of the topped naphtha fraction continuously thereto; heating said topped fraction in the liquid phase in the first heatingzone to its boiling point to depolymerize the dimer; rapidly removing cycloalkadiene monomer formed from said first heating zone; heating the residual liquid portion of the topped naphtha fraction in said second heating zone to a higher boilingpoint-temperature, rapidly removing cycloalkadiene monomer vapor from said second heating zone; fractionating vapors removed from said heating zones in a fractionating .zone which is separate from any zone'in which the initial naphtha fraction is topped to obtain a distillate product of cycloalkadiene monomer free of other close-boiling hydrocarbons.

' HOMER F. JOHNSON, J R.

ReferencesCited in the file of this patent UNITED STATES PATENTS Number Name Date 2,372,237 'Ward Mar. 27, 1945 2,387,993 Hepp Oct. 30, 1945 2,414,651 Latchum, Jr. Jan. 21, 1947 2,511,936 Morrell et a1. June 20, 1950 OTHER REFERENCES Kistiakowsky et al., Jour. Am. Chem. Soc., vol. 58, 148 (1936). 

1. A CONTINUOUS PROCESS FOR FORMING AND SEPARATING A MONOMERIC CYCLOALKADIENE FORM A CRACKED PETROLEUM NAPHTHA FRACTION CONTAINING THE CYCLOALKADIENE DIMER, SAID NAOHTHA FRACTION HAVING BEEN TOPPED TO REMOVE MMOMOMERIC DIOLEFINS AND C7 AND LOWER HYDROCARBONS THAT BOIL BELOW 350* G., WHICH COMPRISES PASSING SAID TOPPED FRACTION CONTAINING SUBSTANTIALLY THE SAME AMOUNT OF THE CYCLOALKADIENE DIMER AS WAS PRESENT IN THE NAPHTHA FRACTION PRIOR TO THE TOP PING TO THE FIRST OF A SERIES OF TWO HEATING ZONES WHERE THIS DIMER UNDERGOES DEPOLYMERIZATION, THE FIRST ZONES BEING COMMUNICATION WITH A SECAND HEATING ZONE SO AS TO SUPPLY A RESIDUAL LIQUID PORTION OF THE TOPPED NAPTHA FRACTION CONTINUOUSLY THERETO; HEATING SAID RESIDUAL LIQUID PORTION FROM THE FIRST HEATING ZONE IN THE LIQUID PHASE IN THE SECOND HEATING ZONE TO DEPOLYMERIZE THE CYCLOALKADIENE DIMER WHICH SAID RESIDUAL LIQUID PORTIONS CONTAINS AND TO FORM VAPOR OF ITS MOMOMER; SWEEPING HOT VAPOR CONTAINING THE MONOMER VAPOR FROM SAID SECOND HEATING ZONE TO SAID FIRST HEATING ZONE STRIP ADDITIONAL CYCLOALKADIENE MONOMER THEREFROM, RAKING OFF THE COMBINED VAPOR FROM SAID FIRST ZONE TO A FRACTIONATION ZONE SEPARATE FROM ANY ZONE IN WHICH INITIAL NAPTHA FRACTION IS TOPPED; FRACTIONATING THE CYCLOALKADIENE MONOMEER FROM THE VAPORS ENTERING SAID FRACTIONATION ZINE IN THE ABSENCE OF C7 AND LOWER HYDROCARBONS OTHER THAN CYCLOALKADIENE MONOMER TO OBTAIN A DISTILLATE PRODUCT OF THE MONOMER, AND RETURNING A BOTTOMS PORTION FROM SAID FRACTIONATION ZONE TO SAID FIRST HEATING ZONE FOR FURTHER RECOVERY OF MONOMERIC CYCLOALKADIENE. 